FIG. 1 depicts a diagram of the salient components of wireless telecommunications system 100 in accordance with the prior art. Wireless telecommunications system 100 comprises: wireless terminal 101, base stations 102-1, 102-2, and 102-3, and wireless switching center 111, interconnected as shown. Wireless telecommunications system 100 provides wireless telecommunications service to all of geographic region 120, in well-known fashion.
In some cases, the owner/operator of wireless telecommunications system 100 might desire to charge its customers different rates depending on where they are at the time that they are using its service. For example, to better compete with land-based wireline telephone service, the owner/operator might desire to charge its customer a lower rate when they are at home and a higher rate when they are out shopping. In this case, the owner/operator might define the customer's home as a geographic “zone” and charge less for calls made from that zone. The efficacy of this idea requires, however, a technique for estimating when a wireless terminal is in a zone and when it is not.
Naturally, if there is a mechanism for ascertaining the location of the terminal (e.g., Global Positioning System [GPS], etc.), then it is a simple matter to determine whether the terminal is inside or outside of a particular zone. However, only a small percentage of wireless terminals presently have built-in GPS receivers, and therefore a GPS-based system is not a viable option. Furthermore, it is well known that GPS receivers do not work well, if at all, indoors and in large cities.
Alternatively, one might use a location system that works with “ordinary” wireless terminals (for example, the system taught in U.S. patent application Ser. No. 11/419,649, entitled “Estimating the Location of a Wireless Terminal Based on Non-Uniform Locations”, filed 22 May 2006, which is incorporated by reference). Such location systems typically involve extensive processing and storage, and are, therefore, deployed within the network infrastructure, rather than on the terminal itself. This approach, however, has two disadvantages. First, it is essentially an “overkill” solution, as it requires substantial (and potentially expensive) processing and storage hardware to solve a different problem than is necessary—estimating the exact location of a terminal—when the problem at hand is estimating whether the terminal is inside a geographic zone. Second, this approach introduces substantial communication overhead between the wireless terminal and the network infrastructure, which is naturally undesirable.
What is needed, therefore, is a technique for estimating whether or not a wireless terminal is inside a zone without some of the costs and disadvantages for doing so in the prior art.